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Plaque Characteristics and Coronary Lesion Physiology
Study Questions:
How do plaque characteristics relate to nonhyperemic indices of coronary stenosis?
Methods:
This is a substudy of the PACIFIC (Prospective Comparison of Cardiac PET/CT, SPECT/CT Perfusion Imaging and CT Coronary Angiography With Invasive Coronary Angiography) trial. One hundred and twenty patients (38% women, age 58.3 ± 8.6 years) and 257 vessels were evaluated. Each patient underwent 256-slice coronary computed tomography (CT) angiography to assess stenosis severity and plaque features (positive remodeling, low attenuation plaque, spotty calcification, and napkin ring sign), as well as intracoronary pressure measurements (fractional flow reserve [FFR], instantaneous wave-free ratio [iFR], Pd/Pa and pressure ratio during adenosine within the wave-free period [iFRa]). CT-derived plaque characteristics were related to these invasive pressure measurements.
Results:
Atherosclerotic plaques were noted in the majority of vessels (66%). On a per-vessel basis, luminal stenosis severity was significantly associated with all measured indices. Multivariable analysis revealed that FFR and iFR were independently related to >70% stenosis (-0.10, p < 0.001 and -0.09, p = 0.003, respectively) and plaque volume (-0.02, p = 0.020 and -0.02, p = 0.030, respectively). Additionally, positive remodeling and spotty calcification were also independent predictors of an impaired FFR (-0.10, p < 0.001 and -0.07, p = 0.021, respectively), but adverse plaque characteristics were not independently related to the vasodilator-free iFR.
Conclusions:
CT-derived plaque characteristics are independently associated with hyperemic flow indices (FFR and iFRa), but not with nonhyperemic indices such as iFR and Pd/Pa. These findings suggest that the effects of hyperemia on pressure-derived indices might depend not only on hemodynamic stenosis severity, but also on plaque characteristics.
Perspective:
The study evaluated the impact of plaque morphology as assessed by CT on hyperemic and nonhyperemic indices of coronary stenosis. The data appear to suggest that abnormal hyperemic indices (FFR and iFRa) predict adverse plaque morphology, whereas resting indices do not. Although it remains unclear as to why or how induction of hyperemia might more reliably predict plaque composition and characteristics compared to resting indices, findings might explain a small proportion of patients who have discordant FFR and iFR values (positive FFR and negative iFR). Overall, the clinical implication of these findings remains unknown without known impact on clinical outcomes. Further study into the proposed relationship between coronary stenosis, plaque morphology, coronary physiology, and clinical events would be useful.
Keywords: Adenosine, Cardiology Interventions, Coronary Artery Disease, Constriction, Pathologic, Coronary Angiography, Coronary Stenosis, Coronary Vessels, Diagnostic Imaging, Fractional Flow Reserve, Myocardial, Hemodynamics, Hyperemia, Perfusion Imaging, Plaque, Atherosclerotic, Tomography, Emission-Computed, Single-Photon, Tomography, X-Ray Computed, Vasodilator Agents
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